This invention relates to a method and apparatus for the treatment of timber products. More specifically, the present invention relates to a method of treating debarked logs by immersing the logs in a hot water bath for an extended time period for the purposes of killing insects and fungi that may be on or in the logs themselves.
In recent years, the demand for timber and wood products made therefrom has been steadily increasing throughout the world. In the United States domestic timber production currently is insufficient to meet this rising level of demand. As a result, timber produced abroad has emerged as a valuable and highly marketable commodity.
Certain insects and fungi can seriously impact the health of forests to the point of killing trees or making the wood undesirable for use. Forests in the United States are not necessarily infested with the same insects and fungi as found in forests of other countries. There is particular concern that imported timber from other countries might introduce new harmful insects or fungi to United States forests.
In order to address these issues, the Plant Protection and Quarantine division of the United States Department of Agriculture has implemented extensive operational guidelines, that apply to foreign timber and timber products that are imported into the United States. These guidelines apply to all hardwood and softwood logs and require certain steps to be performed prior to importation. First, these logs must be debarked. An average of 98% of the bark must be removed with no single log retaining bark on more than 5% of its surface. Next, the center of each debarked log must have been heated to at least 56.degree. C. (approx. 132.8.degree. F.), for thirty minutes. Immediately after the heat treatment, the logs must be safeguarded against reinfestation by either physically protecting or chemically treating the logs. These prophylactic chemical treatments must be repeated at least every thirty days until the logs are shipped to the United States.
Due to the heat transfer and thermal properties of the logs, a significant problem is presented in attempting to bring the center of the log to a temperature of at least 56.degree. C. for thirty minutes, as required by the U.S.D.A. guidelines. Known prior art methods have applied dry heat to logs by raising the temperature of the ambient air surrounding the logs to meet this requirement. Such techniques, however, have suffered from several rather significant drawbacks. Generating the quantity of dry heat needed in order to attain the appropriate internal temperature in the center of a succession of logs of 56.degree. C. for thirty minutes causes a tremendous amount of energy to be consumed. In addition to their high cost of operation, such heat generating sources are costly and time consuming to construct and are often located great distances from where the timber is harvested.
In addition to the energy cost issue, utilization of dry heat in systems as a solution to infestation problems may introduce other new problems into the logs so processed. Kilns or other devices that are used in dry heat treatment of logs generally raise the ambient air surrounding logs to be processed to between 185.degree. and 240.degree., for extended periods of time. It has been found that the application of such high temperature dry heat can cause significant strength losses in many wood species. Such systems have at times had rather detrimental effects on the structural properties of the logs processed thereby, by reducing tensile strength or introducing shrinkage, warping and/or checking.
There has been no use of hot water to treat logs to rid them of insects and harmful fungi in order to meet the U.S.D.A. requirements. There have been uses of heated water for short durations, usually about 35 minutes, but only for the sole stated purpose of loosening the bark for subsequent debarking.
None of these prior art methods has taught submerging completely debarked logs within a hot water bath, for an extended period of time, for the purposes of ridding logs of any infestation or fungi. As such, these prior art hot water methods failed to provide an adequate solution to the problem at hand. As a result, the need exists in the art for a system capable of heating the center of debarked logs to at least 56.degree. C. for thirty minutes in a cost and energy efficient manner that does not significantly weaken or compromise the structural and physical properties of the logs so processed.
Coincidentally, in several regions of the world that have extensive timber resources, such as certain parts of the former Soviet Union, the end of The Cold War has resulted in a vast stockpile of military hardware that is currently completely unused. There is a great desire in countries where this military hardware exists, to attempt to convert the tremendous investment that has already been made in such hardware to productive peacetime commercial uses. Once example of this is the many ships and submarines, that are no longer in service, that have nuclear or fossil fuel power plants that are currently mothballed in ports around the world. A further need therefore exists to adapt such unused military hardware to solve power and heat generation problems.